158 SOIL CONDITIONS AND PLANT GROWTH 



spite of lying not far above the marshes. It contains 45 per cent, of 

 fine sand and therefore tends to cake on the surface after rain and to 

 form steely lumps if worked when wet. Under proper management, 

 however, it produces good crops and is equally suited for ordinary 

 arable and for fruit or potato cultivation. 



The next three soils may be taken as illustrations of the very best 

 loams in the three countries. Silt forms the largest fraction and there- 

 fore the soils possess sufficient, but not too great, a power of retaining 

 water. The fine silt is always lower than the clay ; the latter varies 

 between 12 and 16 per cent., a very satisfactory amount where the 

 rainfall is not too high. As there is a considerable amount of fine 

 sand and no excess of fine silt and clay, the absence of coarse sand is 

 no disadvantage. 



The Tolworth soil is highly productive arable land but almost too 

 heavy for profitable cultivation ; only by dressings of dung (fortunately 

 obtainable cheaply from town) can it be kept workable. It contains 

 rather too much clay and would no doubt have gone down to grass 

 had there not been so much coarse sand present 



The Shaddoxhurst soil is bad. It contains much clay and still 

 more fine silt, consequently its texture is not improved as much as 

 might be expected by liming. There is practically no coarse sand and 

 not much fine sand to keep the soil open, it has always and deservedly 

 been in bad repute. It is best as pasture land, and, after drainage and 

 treatment with basic slag, it may be made useful but never first rate. 



The Ewhurst soils are both in pasture, being too heavy for arable 

 cultivation on account of their high clay and low coarse sand content 

 The first has the better constitution ; silt is the predominant feature, 

 the clay is not too high, nor is the fine silt. It has all the characteristics 

 of a good, if heavy, soil, and is indeed known to be an excellent bullock 

 pasture. The second is not so good ; it contains too much clay and 

 fine silt, and too little silt and coarse sand. It has no great agricultural 

 value. 



Factors Modifying the Interpretation of a Mechanical Analysis. 



The Amount of Organic Matter. Organic matter at the proper 

 stage of decomposition has the effect of binding a loose soil and lighten- 

 ing a heavy one ; thus it reduces the difference between a light sand 

 and a heavy clay, bringing them both closer to the loams. When I o to 

 1 5 per cent, of organic matter is present it so impresses its properties 

 on the soil that the mechanical analysis loses much of its significance, 

 and all the analyst can do is to point out what the soil would become 



